Employing force sensing switches in sensing edges for doors is generally known. Such sensing edges generally include an elongate outer sheath in which a force sensing switch is positioned. Upon the application of force to the sheath, the force sensing switch actuates suitable control circuitry for controlling the movement of the door. The force sensing switch positioned within the sheath typically comprises a pair of flexible, electrically conductive sheets positioned on the upper and lower sides of a layer of nonconducting foam having a plurality of openings extending therethrough from the upper to the lower side. Upon application of force to the sheath, the conductive sheets are deflected into electrically conductive engagement with each other, to thereby actuate suitable control circuitry for controlling the door.
Conventional sensing edges, including the above described switch, are not as sensitive and do not respond as quickly as that contemplated in the present invention. For instance, before the control circuitry is actuated, the conductive sheets must travel the full distance therebetween, in order to make electrical connection. Moreover, if the force applied to the sheath is distributed over a substantial area, the force may, in certain circumstances, not be sufficient to actuate such a switch. Therefore, switches of this type, while sufficient for their intended purpose, may not respond quickly enough to sufficiently protect animate objects in the path of the door from impact damage.
Other types of force sensing switches which can be positioned within the sheath are pressure switches. Such switches typically consist of an elongate tubular member, one end of which is sealingly closed. The other end of the tubular member is in fluid communication with a pressure sensitive switch. The tubular member is longitudinally positioned within the sheath such that upon the application of force to the sheath, pressure within the tubular member is increased and communicated to the pressure sensitive switch to thereby actuate suitable control circuitry for controlling the door.
Although somewhat more sensitive than the first type of force sensing switch discussed previously, the pressure switches still require direct force be applied to the sheath before the control circuitry is actuated. Thus, again, such switches do not respond quickly enough to protect animate objects from the impact of the door.
Employing proximity sensors on door edges to detect the presence of objects in proximity to the door edge is also generally known. Such proximity sensors typically comprise a plurality of local motion detectors spaced closely together along the door edge. Motion near any one detector is detected and suitable control circuitry for controlling the door is actuated. A problem with this type of proximity sensor is that the large number of local motion detectors required make such a sensor costly and difficult to manufacture.
Other types of proximity sensors comprise one or more infrared beams extending from an emitter at one end of the door edge to a detector at the other end of the door edge. The presence of an object in the path of a beam will block the beam from reaching its respective detector thereby actuating the control circuitry. This type of proximity sensor can also be costly since a plurality of beams are needed to detect the presence of objects on all sides of the door edge. Also, manufacturing and adjustment are difficult since each beam must be carefully positioned to fall directly on its respective detector.
A common problem with both types of proximity sensors is that if the sensors fail, no other means of protection is available. Thus, prior art proximity sensors are costly, difficult to manufacture, and do not provide a back-up sensor in the event that the proximity sensor fails.
Consequently, there exists a need for a redundant sensing edge capable of detecting both force applied to the sensing edge, as well as objects in proximity to the sensing edge. Such a redundant sensing edge would fulfill two significant needs. First, the redundancy of the sensing edge would prevent total failure of the sensing edge in the event one of the sensing means ceases to operate. Secondly, the proximity sensing ability of the redundant sensing edge would better protect animate objects from damage by the door since the device is actuated before impact occurs.
The present invention is directed to a redundant sensing edge for a door to protect persons, equipment and the door from impact damage by actuating a device upon detecting an object in proximity to the door edge. The sensing edge of the present invention overcomes the problems inherent in the prior art by incorporating both a force sensing switch and a proximity sensing switch, so that the device can be actuated before actual impact occurs and redundancy is provided in the event that one of the switches ceases to operate. In addition, the proximity sensing switch of the present invention is easier to manufacture and less costly than prior art proximity sensors.